The present invention relates to a fuse in chip design, which is applied to a carrier substrate made of an Al2O3 ceramic, having a fusible metal conductor, which is applied and structured using thin-film technology and is provided with a cover layer, as well as a cost-effective method for manufacturing the chip fuse.
Chip fuses are implemented on a ceramic base material with the aid of methods known to those skilled in the art, such as photolithography. Other carrier materials, such as FR-4 epoxide or polyimide, are also known. Chip fuses are typically designed for a voltage up to 63 V.
In order to avoid damage to other electronic components due to a malfunction in the electrical power supply, which causes over voltage or too large a current flow, providing a fuse in the power supply is known. The fuse essentially comprises a carrier material and a metallic conductor made of copper, aluminium, or silver, for example. The maximum possible current strength which may flow through this conductor without fusing it is determined by the geometry and the cross-section of the conductor. If this value is exceeded, the electrical conductor is fused because of the heat resulting therein due to its electrical resistance and the power supply is thus interrupted before downstream electronic components are overloaded or damaged.
In the methods for manufacturing chip fuses in thick-film technology, in which the fusible element and contact layers are applied as pastes using screen-printing onto a substrate foundation having low thermal conductivity, sufficient precision of the geometry of the fusible element layers may only be implemented inadequately because of the screen-printing method. For high-value thick-layer fuses it is therefore necessary to process the fusible element and/or the fusible metallic conductor through additional laser cutting methods.
Typically, ceramic substrates having a high Al2O3 proportion, which have been glazed over the entire surface, or ceramic substrates, which are low in aluminium oxide, having a low thermal conductivity are selected as the substrate foundation. Both types of substrate are significantly more expensive than typical ceramic substrates made of 96% Al2O3 in thick-film quality, for example, which are used in manufacturing passive components.
In a method for manufacturing a fuse in thin-film technology, a fusible metallic conductor is applied through electrochemical methods or through sputtering. Especially high precision of the cut-off and/or fusing characteristic is achieved in this case through photolithographic structuring of sputtered layers, a substrate low in aluminium oxide having a low thermal conductivity being used as the foundation.
JP 2003/173728 A discloses a manufacturing method for a chip fuse in thin-film technology, a fuse 14 and a cover layer 15 being positioned on a substrate 11. The fuse 14 is structured using photolithography. The substrate 11 has a low thermal conductivity so that it does not dissipate the heat in the electrical conductor 14 caused by current flowing through the electrical conductor 14 and thus favours fusing of the electrical conductor 14. The electrical conductor 14 is in direct contact with the substrate 11.
JP 2002/140975 A describes a fuse having a metallic conductor 14 made of silver, which is also positioned directly on a substrate 11 having low thermal conductivity, the metallic conductor 14 being electroplated or implemented as a thick layer.
JP 2003/151425 A discloses a fuse having a glass ceramic substrate 11 having a low thermal conductivity and a metallic conductor 14 in thick-film technology.
JP 2002/279883 A also describes a fuse for a chip in which the fusible region 17 of the conductor 15 is manufactured through complex laser processing. This requires additional time-consuming and costly processing steps.
JP 2003/234057 A discloses a fuse resistor having a resistor 30 on a substrate 10, a further heat-storing layer 42 being provided between the resistor 30 and the substrate 10 in order to store the heat arising in the resistor 30. The fusible region is also manufactured through laser processing.
JP 08/102244 A describes a fuse 10 in thick-film technology having a glass glaze layer 2 having a low thermal conductivity, the glass layer 2 being positioned on a ceramic substrate 1 and a fuse 3 being applied to the glass layer 2.
JP 10/050198 A discloses a further fuse in thin-film technology having a complex layer construction, in which a further elastic silicone layer 6 is implemented on the conductor 3 and a glass layer 5.
DE 197 04 097 A1 describes an electrical fuse element having a fusible conductor in thick-film technology and a carrier, the carrier comprising a material having poor thermal conductivity, particularly a glass ceramic.
DE 695 12 519 T2 discloses a surface-mounted fuse device, a thin-film fusible conductor being positioned on a substrate and the substrate preferably being an FR-4 epoxide or a polyamide.
Therefore, a method is known for manufacturing chip fuses in thick-film technology using special ceramics or even Al2O3 ceramics and a thermally insulating intermediate layer, and chip fuses in thin-film technology using special ceramics or other special carrier materials are also known.